public class leijia {
    public static void main(String[] args) {
        double h=0;
        for(double i = 1;i <= 100;i++){
            if(i%2==0){
                h -= 1/i;
            }
            else{
                h += 1/i;
            }
        }
        System.out.println(h);
    }
}
